The present invention relates to the winding of textile yarns into core supported packages, and more particularly the random winding of a cylindrical cross wound package of a textured yarn, such as a false twist textured filament yarn. In such winding operations, the end faces of the cylindrical package may lie in a normal plane (winding with straight end faces), or the end faces may be inclined relative to this normal plane (biconical winding).
A randomly cross wound package in the context of the present invention is a cross wound package having a winding ratio which constantly varies during the course of the winding cycle. The "winding ratio" is here understood to mean the ratio of the package speed (revolutions of the package per minute) to the traversing speed (number of double strokes per minute). Packages of the described type are described in DIN No. 61800 (German Industrial Standards), and they are commonly produced on the winding systems of yarn texturing machines. In such machines, the yarns receive crimp-elastic properties from their treatment, in particular the false twist texturing operation.
It is known that the end areas on the peripheral surface of cross wound packages often include bulges which result from an unavoidable deposit of an unduly large quantity of yarn in the area of stroke reversal. In order to avoid such bulges at the package ends, it is known to periodically modify the traverse stroke, by a periodic shortening and lengthening of the stroke in the area of these bulges. It is also known that pattern or ribbon breaking steps should be employed in the production of cross wound packages. A ribbon may be described as an appearance on the package, where in successively wound layers of the yarn, uni-directional yarn lengths more or less overlie each other. Such ribbons are normally avoided in that the traverse speed, which is expressed as the number of reciprocal movements (double strokes) of the traversing yarn guide, is decreased and increased between an upper and a lower limit.
It is also known that the tension at which the yarn is wound on the package, is an important factor for good unwinding properties. In particular, it is important that the tension be uniform over the yarn length and the length of the package. To ensure a uniform yarn tension, it is known that a stroke modification and a pattern breaking may occur simultaneously in such a manner that changes of the traverse speed which result from changes of the stroke of the traversing yarn guide, are compensated for by the changes which are caused for the purpose of breaking a pattern.
From investigations as to the unwinding behavior of packages, it has surprisingly been found that a flattening of the cylindrical surface area of the cross wound package on the end opposite to the unwinding end of the package, results in substantially improved unwinding properties of the yarn. In this regard, such packages are commonly mounted on a creel, with the yarns being withdrawn in an axial direction over one end of the package. The unwinding end of the package is usually identified by a rounded edge on the supporting core or bobbin tube, and a yarn transfer tail which is used to connect the beginning of a yarn on one package with the end of a yarn on a successive package, is positioned at the opposite end, i.e. the end opposite the unwinding end.
As noted above, a flattening of the surface area on the end opposite the unwinding end results in improved unwinding properties. In contrast thereto, bulged formations on the unwinding end of the package, have no disadvantageous unwinding consequences. This result was totally unexpected, inasmuch as the opposite result would have been expected from experience with the unwinding behavior of yarns from conical packages.
It should also be noted that the flattening of the cylindrical surface of the cross wound package in accordance with the present invention is not an inclined face, as is obtained in the production of biconical, cross wound packages by uniformly shortening the stroke of the traverse guide. Rather, the flattening is an intentionally produced uniform reduction of the diameter on at least the end of the cylindrical package which is opposite to the unwinding end of the package. Thus in packages which have a transfer tail, a flattened portion is provided on the end of the package where the transfer tail is located. Such packages may be produced in a winding system with means for a periodic contraction and lengthening of the stroke of the traversing yarn guide (i.e. stroke modification), together with a ribbon breaking mechanism. The length of the modified strokes may be substantially decreased, for example, to about 22 mm contraction of the stroke at one or both ends of a basic stroke of the traversing yarn guide of about 250 mm. U.S. Pat. No. 4,325,517 discloses a winding process of this general type.
Packages which are produced in the above manner have however, relatively soft frontal surfaces. Depending on the type of further processing, the soft surfaces are undesirable since they are more easily damaged than hard packages. Thus in many instances, and in particular because of the resulting transport and handling problems, such packages have proven to be undesirable despite their favorable unwinding properties.
In copending and commonly owned U.S. patent application Ser. No. 765,709, now U.S. Pat. No. 4,659,027 a winding method and apparatus is disclosed which maintains the advantage of packages with flattened ends while avoiding unduly soft package ends. Thus a package may be produced having a desirable hardness and with excellent unwinding properties. More particularly the referenced copending application discloses a winding process wherein the yarn traverse guide is controlled to define a series of stroke modification cycles having a sawtooth-like configuration when the end points of the strokes are plotted against time, and wherein a number of stroke modification cycles having a relatively large contraction alternate with cycles having a relatively small contraction. In addition, the speed of the yarn guide may be constantly accelerated and decelerated to avoid undesirable patterns.
In accordance with the present invention, the advantages of packages with flattened ends are maintained. In addition, unduly soft packages are avoided, and a package with a desired controlled hardness together with excellent unwinding properties is produced. Further, the present invention controls the shape of the package, and it is not only possible to avoid the bulges which normally appear on the cylindrical surface of the package, and the invention provides an accurate cylindrical surface in the stroke reversal areas. The present invention thus represents an advance from the method disclosed in U.S. Pat. No. 4,325,517, and copending application Ser. No. 765,709, in which the length of the traverse stroke is varied.
It is accordingly an object of the present invention to provide a method for winding yarns which is adapted to provide substantial uniformity in the package build, and satisfactory unwinding properties.
It is also an object of the present invention to provide a method for winding yarn which is adapted to provide an even mass distribution of the yarn in the stroke reversal area and such that a cylindrical surface is obtained.
It is a further object of the present invention to provide a method for winding a yarn by a variable traverse stroke, and without the need for unduly high accelerations and decelerations of the traverse stroke mechanism.
It is a more particular object of the present invention to provide a method for winding yarns which is adapted to produce a package of relatively large diameter, and yet which insures a satisfactory overhead withdrawal of the yarn at high unwinding speeds, of for example, 1000 m/min or greater, and wherein the package has a stable, cylindrical shape, and which is wound under a uniform tension irrespective of the modified traverse motions and pattern breaking steps.